Add .gitattributes files

We should add proper `.gitattributes` files to all repositories and exclude unneeded files to make the distributions smaller.
eg:

```
tests/ export-ignore
.gitattributes export-ignore
.gitignore export-ignore
.travis.yml export-ignore
.check-author.yml export-ignore
composer.lock export-ignore
phpunit.xml.dist export-ignore
build.default.properties export-ignore
build.xml export-ignore
```
